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Synthesis 1993; 1993(4): 390-394
DOI: 10.1055/s-1993-25870
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Synthesis of New 3,4-Disubstituted 2,5-Dihydro-1H-pyrrol-1-yloxyl Spin-Label Reagents via Allylic Rearrangements

Kálmán Hideg* , Cecília P. Sár, Olga H. Hankovszky, Tünde Tamás, Gyula Jerkovich
  • *Central Research Laboratory, Chemistry, University of Pécs, H-7643 Pécs, PO Box 99, Hungary
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Publication Date:
17 September 2002 (online)

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Several 3,4-disubstituted 2,5-dihydro-1H-pyrrol-1-yloxyl radicals were synthesized. 2,5-Dihydro-3-hydroxymethyl-2,2,5,5-tetramethyl-1H-pyrrol-1-yloxyl radical (1) was reacted with triethyl orthoacetate in a Claisen rearrangement to give the exoolefinic compound 2. This was converted to its 1-acetoxyl derivative 3, which was then brominated in the allylic position. Subsequent rearrangement gave the endoolefinic compound 1-acetoxyl-4-bromomethyl-3-ethoxycarbonylmethyl-2,2,5,5-tetramethyl-1H-pyrrole radical (4). The allylic bromine could be replaced with nucleophiles (NaSCN, KSeCN, thiourea, selenourea, NaN3 and KSSO2Me) to give 5a-e and 26. The diamagnetic thiocyanates and selenocyanates could be reduced with sodium borohydride to the free thiol and selenol monoradicals, which were oxidized to reversible, ester-functionalized disulfide or diselenide diradical reagents 24 and 25.